Effects of TiO2 dosage, pH and temperature on decolorization of C.I. Reactive Red 2 in a UV/US/TiO2 system

This study elucidates the decolorization of C.I. Reactive Red 2 (RR2) in ultrasound (US), US/TiO(2), ultraviolet (UV)/TiO(2) and UV/US/TiO(2) systems. The effects of TiO(2) dosage, pH and temperature on RR2 decolorization were determined in a UV/US/TiO(2) system. The pseudo-first-order decolorization rate constants of 0.5, 1 and 2g/l TiO(2) in the UV/US/TiO(2) system were 0.45, 0.57 and 0.94 h(-1), respectively. In the UV/US/TiO(2) system, the decolorization rate of RR2 declines as pH increases, and increases as temperature increasing. At pH 7, the decolorization rates followed the order of UV/US/TiO(2) (0.94 h(-1))>UV/TiO(2) (0.85h(-1))>US/TiO(2) (0.25 h(-1))>US. The activation energy of the UV/US/TiO(2) system at pHs of 4, 7 and 10 was 6.58, 11.62 and 21.32kJ/mol, respectively. Experimental results suggest that the RR2 decolorization in the UV/US/TiO(2) system was a diffusion-controlled reaction.